The present invention relates to a method of forming a tungsten silicide film used mainly in the manufacture of a semiconductor device, particularly, the tungsten silicide film used for forming a gate electrode/wiring in combination with, for example, a polycrystalline silicon layer and a method of forming the same.
A so-called "polyside structure", in which, for example, a polycrystalline silicon layer and a tungsten silicide layer are superposed one upon the other, is used for forming a gate electrode and a wiring in a semiconductor device such as LSI in order to lower the resistance of the gate electrode and the wiring. In this case, the tungsten silicide layer constituting the upper layer of the polyside structure is formed in general by a CVD method using WF.sub.6 /SiCl.sub.2 H.sub.2 /Ar as a process gas. In the conventional film forming method, the required properties of the tungsten silicide layer are obtained by controlling the film forming temperature, the pressure of the process gas, the gas flow rate, the flow rate ratio of the gases, etc. Also, it is known to the art that, in order to control the resistivity of the tungsten silicide layer and to increase the resistance to migration, it is necessary to control the crystal grain diameter and the crystal orientation of the tungsten silicide layer.
In the conventional method of forming a tungsten silicide layer, however, it was impossible to control as desired the crystal grain diameter and the crystal orientation of the tungsten silicide layer. For example, the tungsten silicide film formed by the conventional method is large in nonuniformity of the crystal grain diameter. Also, concerning the crystal orientation, (002) faces and (101) faces are present in substantially the same rate. It follows that it is difficult to control the crystal grain diameter and the crystal orientation, leading to the problem that the crystals after the heat treatment are oriented at random.